In compact brake caliper units of rail vehicles, the wear of the brake linings and of the brake disk is compensated automatically by lengthening or shortening a push rod or pull rod adjuster. The lengthening or shortening of the actuator is carried out by a helical gearing as a nut-spindle system. To achieve the greatest possible adjustment per activation, the thread is embodied with a very large pitch. The thread is therefore not self-locking. While the one helical gear element, for example the nut, is secured in a rotationally fixed fashion, the other helical gear element, for example the spindle, is rotatably mounted.
An actuation mechanism enables an actuator lever with a freewheeling mechanism (for example sleeve freewheeling mechanism) to be rotated, which actuator lever in turn drives or rotates the spindle or the nut of the push rod adjuster in such a way that the actuator in the case of a push rod adjuster is, for example, lengthened. For the purpose of adjustment, the actuator lever is therefore activated by a push rod with a spherical head, which push rod engages in a dome of the actuator lever. The spindle is rotated along by the sleeve freewheeling mechanism which is pressed into the actuator lever. In this context, a wrap spring freewheeling mechanism slips through in the freewheeling direction. If the push rod releases the actuator lever again when the brake is released, the actuator lever is rotated back again into its home position by a restoring spring, in which home position the actuator lever abuts against a rigid stop of the adjustor housing. The sleeve freewheeling mechanism rotates here in a freewheeling direction, and in the process the spindle is prevented from rotating along by the wrap spring of the wrap spring freewheeling mechanism. The adjustment process is ended when the actuator lever abuts against a stop in the adjustor housing or when an axial force which can no longer be overcome by the actuation mechanism of the actuator builds up in the actuator, for example when the linings come to bear on the brake disk.
In the case of a push rod adjuster, a rotation, for example, of the spindle of the spindle-nut gear mechanism in the direction which shortens the push rod adjuster is prevented by a wrap spring freewheeling mechanism between the spindle and the adjustor housing. This wrap spring freewheeling mechanism forms, in addition to the freewheeling mechanism of the actuator element, a further or second freewheeling mechanism. As a result of the wrap spring freewheeling mechanism, the rotatable spindle is held in its position when the actuator element is rotated back into its home position by the force of its restoring spring and/or if a large brake application force acts on the actuator, and therefore a large torque acts on the spindle, during a braking operation.
EP 0 732 247 B1 describes a push rod adjuster of a brake caliper of a disk brake of a rail vehicle in which, according to FIG. 3, the nut is secured in a rotationally fixed fashion in the right-hand wear adjuster housing (reference number 22) and the spindle is rotatably mounted in a guide tube which is connected to the left-hand wear adjuster housing (reference number 21). Furthermore, there is a wrap spring freewheeling mechanism which blocks in the direction of rotation of the spindle counter to a wear adjustment and freewheels in the opposite direction of rotation, it being possible to couple the spindle, by the wrap spring freewheeling mechanism, to the separate guide tube which is secured to the left-hand wear adjuster housing. A wrap spring of the wrap spring freewheeling mechanism is enclosed radially here by the left-hand wear adjuster housing which also accommodates the actuator lever (reference number 24) and the sleeve freewheeling mechanism.
The axial force which loads the push rod adjuster when the brakes are activated, and which attempts to shorten the push rod actuator is supported in the force flux from the rotationally fixed nut, and the threaded spindle is supported by the actuator lever in the left-hand wear adjuster housing. As a result, the actuating accuracy of the wear adjuster is influenced not only by the thread friction of the helical gearing but also by the frictional conditions between the actuator lever and the left-hand wear adjuster housing or between the actuator lever and the threaded spindle.
EP 0 699 846 B1 describes a disk brake for rail vehicles have a brake caliper and an automatic wear adjuster. In the embodiment as a push rod actuator which is described in the document, the actuator lever is formed by an actuator sleeve with outer toothing. A sleeve freewheeling mechanism is pressed into this actuator sleeve. A gearwheel segment, by which the actuator sleeve can be rotated counter to the force of a restoring spring by a lever, is in engagement with the toothing of the actuator sleeve. The nut is entrained by the sleeve freewheeling mechanism, as a result of which the push rod adjuster is lengthened. According to FIG. 2, the spindle is mounted here in a rotationally fixed fashion in the left-hand wear adjustor housing, and the nut is mounted in a rotatable fashion in the right-hand wear adjuster housing. By a wrap spring of a wrap spring freewheeling mechanism, the rotatable nut can be secured to a radially inner tube part (reference number 29), which is connected to the right-hand wear adjuster housing. Furthermore, a tube-like housing part (reference number 30) of the right-hand wear adjuster housing encloses the wrap spring freewheeling mechanism.
In the described push rod adjusters of the prior art, in each case at least one wear adjuster housing is constructed in multiple parts and, in particular, in the manner of a double tube by virtue of the fact that the wrap spring of the wrap spring freewheeling mechanism interacts with a separate tube, which is connected to the respective wear adjuster housing, and, on the other hand, the wrap spring freewheeling mechanism is respectively radially enclosed by a tube-like projection of this wear adjuster housing. However, the construction of such a double-tube-like wear adjuster housing entails certain costs for the manufacture and assembly or disassembly for repair purposes.
Furthermore, the space required for connecting the separate tubes to the respective wear adjuster housing reduces the installation space for the wrap spring freewheeling mechanism, for which reason the wrap spring in the described prior art has to be secured to the rotationally fixed and separate tube by a hook. However, such a hook has an unfavorable effect on the switching accuracy of the wrap spring freewheeling mechanism and therefore on the actuating accuracy of the wear adjuster. Furthermore, a separate step for manufacturing the hook is also necessary during fabrication.